Heat exchange with compressed gas in energy-storage systems

ABSTRACT

In various embodiments, compressed-gas energy storage and recovery systems include a cylinder assembly for compression and/or expansion of gas, a reservoir for storage and/or supply of compressed gas, and a system for thermally conditioning gas within the reservoir.

RELATED APPLICATIONS

This application (A) claims the benefit of and priority to U.S.Provisional Patent Application No. 61/328,408, filed Apr. 27, 2010; (B)is a continuation-in-part of U.S. patent application Ser. No.12/690,513, filed Jan. 20, 2010, which claims priority to U.S.Provisional Patent Application No. 61/145,860, filed on Jan. 20, 2009,U.S. Provisional Patent Application No. 61/145,864, filed on Jan. 20,2009, U.S. Provisional Patent Application No. 61/146,432, filed on Jan.22, 2009, U.S. Provisional Patent Application No. 61/148,481, filed onJan. 30, 2009, U.S. Provisional Patent Application No. 61/151,332, filedon Feb. 10, 2009, U.S. Provisional Patent Application No. 61/227,222,filed on Jul. 21, 2009, U.S. Provisional Patent Application No.61/256,576, filed on Oct. 30, 2009, U.S. Provisional Patent ApplicationNo. 61/264,317, filed on Nov. 25, 2009, and U.S. Provisional PatentApplication No. 61/266,758, filed on Dec. 4, 2009; and (C) is acontinuation-in-part of U.S. patent application Ser. No. 12/639,703,filed Dec. 16, 2009, which (i) is a continuation-in-part of U.S. patentapplication Ser. No. 12/421,057, filed Apr. 9, 2009, which claims thebenefit of and priority to U.S. Provisional Patent Application No.61/148,691, filed Jan. 30, 2009, and U.S. Provisional Patent ApplicationNo. 61/043,630, filed Apr. 9, 2008; (ii) is a continuation-in-part ofU.S. patent application Ser. No. 12/481,235, filed Jun. 9, 2009, whichclaims the benefit of and priority to U.S. Provisional PatentApplication No. 61/059,964, filed Jun. 9, 2008; and (iii) claims thebenefit of and priority to U.S. Provisional Patent Application No.61/166,448, filed on Apr. 3, 2009; 61/184,166, filed on Jun. 4, 2009;61/223,564, filed on Jul. 7, 2009; 61/227,222, filed on Jul. 21, 2009;and 61/251,965, filed on Oct. 15, 2009. The entire disclosure of each ofthese applications is hereby incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

This invention was made with government support under IIP-0810590 andIIP-0923633 awarded by the NSF. The government has certain rights in theinvention.

FIELD OF THE INVENTION

In various embodiments, the present invention relates to pneumatics,power generation, and energy storage, and more particularly, tocompressed-gas energy-storage systems and methods using pneumatic orpneumatic/hydraulic cylinders, as well as to the heating and cooling ofstored compressed gas in such systems.

BACKGROUND

Storing energy in the form of compressed gas has a long history andcomponents tend to be well tested and reliable, and have long lifetimes.The general principle of compressed-gas or compressed-air energy storage(CAES) is that generated energy (e.g., electric energy) is used tocompress gas (e.g., air), thus converting the original energy topressure potential energy; this potential energy is later recovered in auseful form (e.g., converted back to electricity) via gas expansioncoupled to an appropriate mechanism. Advantages of compressed-gas energystorage include low specific-energy costs, long lifetime, lowmaintenance, reasonable energy density, and good reliability.

If a body of gas is at the same temperature as its environment, andexpansion occurs slowly relative to the rate of heat exchange betweenthe gas and its environment, then the gas will remain at approximatelyconstant temperature as it expands. This process is termed “isothermal”expansion. Isothermal expansion of a quantity of gas stored at a giventemperature recovers approximately three times more work than would“adiabatic expansion,” that is, expansion where no heat is exchangedbetween the gas and its environment—e.g., because the expansion happensrapidly or in an insulated chamber. Gas may also be compressedisothermally or adiabatically.

An ideally isothermal energy-storage cycle of compression, storage, andexpansion would have 100% thermodynamic efficiency. An ideally adiabaticenergy-storage cycle would also have 100% thermodynamic efficiency, butthere are many practical disadvantages to the adiabatic approach. Theseinclude the production of higher temperature and pressure extremeswithin the system, heat loss during the storage period, and inability toexploit environmental (e.g., cogenerative) heat sources and sinks duringexpansion and compression, respectively. In an isothermal system, thecost of adding a heat-exchange system is traded against resolving thedifficulties of the adiabatic approach. In either case, mechanicalenergy from expanding gas must usually be converted to electrical energybefore use.

An efficient and novel design for storing energy in the form ofcompressed gas utilizing near isothermal gas compression and expansionhas been shown and described in U.S. Pat. No. 7,832,207 (the '207patent) and U.S. patent application Ser. No. 12/639,703 (the '703application), the disclosures of which are hereby incorporated herein byreference in their entireties. The '207 patent and the '703 applicationdisclose systems and methods for expanding gas isothermally in stagedcylinders and intensifiers over a large pressure range in order togenerate electrical energy when required. Mechanical energy from theexpanding gas may be used to drive a hydraulic pump/motor subsystem thatproduces electricity. Systems and methods for hydraulic-pneumaticpressure intensification that may be employed in systems and methodssuch as those disclosed in the '207 patent and the '703 application areshown and described in U.S. patent application Ser. No. 12/879,595 (the'595 application), the disclosure of which is hereby incorporated hereinby reference in its entirety.

In the systems disclosed in the '207 patent and the '703 application,reciprocal mechanical motion is produced during recovery of energy fromstorage by expansion of gas in the cylinders. This reciprocal motion maybe converted to electricity by a variety of means, for example asdisclosed in the '595 application as well as in U.S. patent applicationSer. No. 12/938,853 (the '853 application), the disclosure of which ishereby incorporated herein by reference in its entirety. The ability ofsuch systems to either store energy (i.e., use energy to compress gasinto a storage reservoir) or produce energy (i.e., expand gas from astorage reservoir to release energy) will be apparent to any personreasonably familiar with the principles of electrical and pneumaticmachines.

The efficiency, cost effectiveness, and performance of compressed-airenergy storage systems can be improved through subsystems designed foreffective heat transfer to and from the gas being, respectively,expanded and compressed. Additionally, pre-heating of stored compressedgas during expansion, which can employ low-grade process heat or evenheat from the ambient environment, effectively increases the energystored in a given volume at a given pressure and can improvecompressed-air energy storage system efficiency and/or power output.

SUMMARY

Embodiments of the present invention feature compressed-gasenergy-conversion systems that include one or more reservoirs (e.g.,pressure vessels or naturally occurring or artificially createdformations such as caverns) for storage of the compressed gas, as wellas a heat-exchange subsystem for thermal conditioning (i.e., heatingand/or cooling, in many embodiments for maintaining of a substantiallyconstant temperature during, e.g., storage and/or processing (e.g.,transfers into and/or out of a system component and/or compressionand/or expansion within a component)) the gas within the reservoir. Thepower output of such compressed-gas energy-storage-and-recovery systemsmay be governed, at least in part, by the pressure and volumetric rateof compressed-air expansion and by the temperature of the expanded gas.The round-trip efficiency of the system is also influenced by the energyconsumed during compression, which is minimized by compressingisothermally (less work is required to compress a quantity of gas thatstays at a constant temperature than one that gets hotter as it iscompressed). Therefore, the ability to expand and compress the gasisothermally or near-isothermally at a faster rate will result ingreater power output for the system while maintaining the total energyoutput—considering expansion gains alone—at nearly triple that of asystem using adiabatic expansion.

Preheating a certain mass of compressed air in a fixed volume orreservoir, such as one or more pressure vessels or caverns, willgenerally increase the pressure of the compressed air and thus thestored potential energy. Upon expansion, more energy will be recoveredfrom the compressed air, essentially recovering energy from the heatsource (e.g., waste heat, process heat, ground loop); also, the finaltemperature of the expanded air will be higher than when the initialcompressed air is at ambient temperature. Likewise, cooling of thestored compressed gas will generally decrease the pressure in thereservoir and thus reduce the work necessary to compress more gas intothem. When the stored compressed gas later increases in temperature(e.g., through preheating), the energy stored in the reservoir willincrease. Thus, by pre-cooling the compressed gas and/or cooling the gasduring compression, less energy will be required in the compressionphase. These principles are advantageously harnessed in the systemsdepicted in the figures and detailed below.

Embodiments of the invention combine systems and techniques for heatingand cooling compressed gas with the aforementioned compressed-gasenergy-storage systems to enable cost-effective, efficient energystorage. In various embodiments, a heat-exchange subsystem is used tofacilitate and expedite heat transfer to (from) stored compressed gasprior to and during gas expansion (compression) of the compressed-gasenergy storage system. The heat-exchange subsystem may be combined withthermal systems to increase power density and efficiency by utilizingthe thermal systems to chill or heat the transfer medium (e.g., water)and thereafter the compressed gas. In one application, excess thermalenergy (waste heat) from power plants or industrial processes is used topreheat the compressed gas in the heat-exchange subsystem of thecompressed-gas energy-storage system. In such cases, the effective powerdensity of the energy storage system may be increased further by usingit to heat the gas during expansion of stored gas. Similarly, chilledwater, such as may be available at low cost from the local environment(e.g., from a river), may be used to pre-cool the stored compressed gasprior to further compression and cool the compressed gas duringcompression, decreasing power requirements during compression. In theabsence of such heating or cooling sources, heated and chilled water maybe efficiently generated using ground loops, water loops, heat pumps orother means.

In various embodiments, the invention relates to the combination oflocal sources or sinks of thermal energy to increase the effective powerdensity and storage capacity of a compressed-gas energy storage system.Management of such sources and sinks may include recovering wastethermal energy from an installation (e.g., industrial process) toincrease power output during or prior to gas expansion or rejectingthermal energy to the environment (e.g., via river water, chillers, heatexchangers) to decrease power input during or prior to gas compression.In one embodiment, power from an electric generating plant is stored,and the storage system's power output is increased using heat from thegenerating plant that would otherwise be wasted (i.e., lost) to theenvironment. The installation supplying heat to the compressed gas priorto and during expansion may be a fossil-fuel based power plant, aheat-engine based power plant, a nuclear power plant, a geothermalsystem, an industrial process producing waste heat, a heat pump, or asource of cold water. In power plant applications, the generated powermay be used to drive the compressed-gas energy storage system, producingcompressed gas, which is then stored in at least one pressure vessel orother reservoir.

Embodiments of the present invention are typically utilized in energystorage and generation systems utilizing compressed gas. In acompressed-gas energy storage system, gas is stored at high pressure(e.g., approximately 3,000 psi). This gas may be expanded into acylinder having a first compartment (or “chamber”) and a secondcompartment separated by a piston slidably disposed within the cylinder(or other boundary mechanism). A shaft may be coupled to the piston andextend through the first compartment and/or the second compartment ofthe cylinder and beyond an end cap of the cylinder, and a transmissionmechanism may be coupled to the shaft for converting a reciprocal motionof the shaft into a rotary motion, as described in the '595 and '853applications. Moreover, a motor/generator may be coupled to thetransmission mechanism. Alternatively or additionally, the shaft of thecylinders may be coupled to one or more linear generators, as describedin the '853 application.

As also described in the '853 application, the range of forces producedby expanding a given quantity of gas in a given time may be reducedthrough the addition of multiple, series-connected cylinder stages. Thatis, as gas from a high-pressure reservoir is expanded in one chamber ofa first, high-pressure cylinder, gas from the other chamber of the firstcylinder is directed to the expansion chamber of a second,lower-pressure cylinder. Gas from the lower-pressure chamber of thissecond cylinder may either be vented to the environment or directed tothe expansion chamber of a third cylinder operating at still lowerpressure; the third cylinder may be similarly connected to a fourthcylinder; and so on.

The principle may be extended to more than two cylinders to suitparticular applications. For example, a narrower output force range fora given range of reservoir pressures is achieved by having a first,high-pressure cylinder operating between, for example, approximately2,500 psig and approximately 50 psig and a second, larger-volume,lower-pressure cylinder operating between, for example, approximately 50psig and approximately 1 psig. When two expansion cylinders are used,the range of pressure within either cylinder (and thus the range offorce produced by either cylinder) is reduced as the square rootrelative to the range of pressure (or force) experienced with a singleexpansion cylinder, e.g., from approximately 2500:1 to approximately50:1 (as set forth in the '853 application). Furthermore, as set forthin the '595 application, N appropriately sized cylinders can reduce anoriginal operating pressure range R to R^(1/N). Any group of N cylindersstaged in this manner, where N≧2, is herein termed a cylinder group.

All of the approaches described above for converting potential energy incompressed gas into mechanical and electrical energy may, ifappropriately designed, be operated in reverse to store electricalenergy as potential energy in a compressed gas. Since the accuracy ofthis statement will be apparent to any person reasonably familiar withthe principles of electrical machines, power electronics, pneumatics,and the principles of thermodynamics, the operation of these mechanismsto both store energy and recover it from storage will not be describedfor each embodiment. Such operation is, however, contemplated and withinthe scope of the invention and may be straightforwardly realized withoutundue experimentation.

Embodiments of the invention may be implemented using any of theintegrated heat-transfer systems and methods described in the '703application and/or with the external heat-transfer systems and methodsdescribed in the '426 patent. In addition, the systems described herein,and/or other embodiments employing liquid-spray heat exchange orexternal gas heat exchange, may draw or deliver thermal energy via theirheat-exchange mechanisms to external systems (not shown) for purposes ofcogeneration, as described in U.S. patent application Ser. No.12/690,513, filed Jan. 20, 2010 (the '513 application), the entiredisclosure of which is incorporated by reference herein.

The compressed-air energy storage and recovery systems described hereinare preferably “open-air” systems, i.e., systems that take in air fromthe ambient atmosphere for compression and vent air back to the ambientafter expansion, rather than systems that compress and expand a capturedvolume of gas in a sealed container (i.e., “closed-air” systems). Thus,the systems described herein generally feature one or more cylinderassemblies for the storage and recovery of energy via compression andexpansion of gas. Selectively fluidly connected to the cylinder assemblyare (i) means for storage of compressed gas after compression and supplyof compressed gas for expansion thereof, and (ii) a vent for exhaustingexpanded gas to atmosphere after expansion and supply of gas forcompression. The means for storage of compressed gas may include orconsist essentially of, e.g., one or more pressure vessels or naturallyoccurring formations such as caverns or other large cavities. Open-airsystems typically provide superior energy density relative to closed-airsystems.

Furthermore, the systems described herein may be advantageously utilizedto harness and recover sources of renewable energy, e.g., wind and solarenergy. For example, energy stored during compression of the gas mayoriginate from an intermittent renewable energy source of, e.g., wind orsolar energy, and energy may be recovered via expansion of the gas whenthe intermittent renewable energy source is nonfunctional (i.e., eithernot producing harnessable energy or producing energy atlower-than-nominal levels). As such, the systems described herein may beconnected to, e.g., solar panels or wind turbines, in order to store therenewable energy generated by such systems.

In one aspect, embodiments of the invention feature a compressed-gasenergy storage and recovery system that includes or consists essentiallyof a cylinder assembly for compressing gas to store energy and/orexpanding gas to recover energy, a compressed-gas reservoir for storageof gas after compression and supply of compressed gas for expansion, anda heat-exchange subsystem for thermally conditioning gas within thecompressed-gas reservoir via heat exchange between the gas and aheat-exchange fluid not in fluid communication with the gas. Thecompressed-gas reservoir is selectively fluidly connected to thecylinder assembly.

Embodiments of the invention may feature one or more of the following,in any of a number of combinations. The compressed-gas reservoir mayinclude or consist essentially of a plurality of pressure vessels. Theheat-exchange subsystem may circulate the heat-exchange fluid aroundeach of the pressure vessels to exchange heat through a wall thereofwith gas in the pressure vessels. The plurality of pressure vessels maybe disposed in an enclosure, and the heat-exchange fluid may becirculated through the enclosure. The heat-exchange fluid may include orconsist essentially of a liquid, e.g., water. The pressure vessels maybe submerged in the heat-exchange fluid. The heat-exchange fluid mayinclude or consist essentially of a heat-exchange gas, e.g., air (forexample atmospheric air). The enclosure may comprise an opening therein,and the heat-exchange subsystem may include or consist essentially of afan for drawing the heat-exchange gas into the enclosure through theopening.

The heat-exchange subsystem may include a heat exchanger, through whichthe heat-exchange fluid is circulated, for maintaining the heat-exchangefluid at a substantially constant temperature. The heat-exchangesubsystem may include a conduit, disposed within the compressed-gasreservoir, through which the heat-exchange fluid is circulated duringheat exchange between the heat-exchange fluid and the gas. The conduitmay include one or more fins thereon for expediting the heat exchange.The heat-exchange fluid may include or consist essentially of a liquid,e.g., water. A fluid reservoir may be in fluid communication with theconduit, and heat-exchange fluid may be circulated from the fluidreservoir, through the conduit, and back to the fluid reservoir.

A vent for exhausting expanded gas to atmosphere and supply of gas forcompression thereof may be selectively fluidly connected to the cylinderassembly. An intermittent renewable energy source (e.g., of wind orsolar energy) may be connected to the cylinder assembly. Energy storedduring compression of the gas may originate from the intermittentrenewable energy source, and/or energy may be recovered via expansion ofthe gas when the intermittent renewable energy source is nonfunctional.A movable boundary mechanism (e.g., a piston) may separate the cylinderassembly into two chambers. A crankshaft for converting reciprocalmotion of the boundary mechanism into rotary motion may be mechanicallycoupled to the boundary mechanism. A motor/generator may be coupled tothe crankshaft.

The system may include a second heat-exchange subsystem (which may beseparate and different from the heat-exchange system) for thermallyconditioning gas in the cylinder assembly (e.g., during the compressionand/or expansion), thereby increasing efficiency of the energy storageand recovery. The heat-exchange subsystem and the second heat-exchangesubsystem may both utilize the heat-exchange fluid for heat exchange(e.g., by spraying it within the compressed-gas reservoir and thecylinder assembly, respectively). The system may include an externalheating or cooling source (e.g., a thermal well) for maintaining theheat-exchange fluid at a substantially constant temperature. Theexternal heating or cooling source may include or consist essentially ofa fossil fuel power plant, a heat engine power plant, a solar thermalsource, a geothermal source, an industrial process with waste heat, aheat pump, a heat source, a heat sink, and/or a source ofenvironmentally chilled water.

In another aspect, embodiments of the invention feature a compressed-gasenergy storage and recovery system including or consisting essentiallyof a cylinder assembly for compressing gas to store energy and/orexpanding gas to recover energy, a compressed-gas reservoir for storageof gas after compression and supply of compressed gas for expansion, anda heat-exchange subsystem for thermally conditioning gas within thecompressed-gas reservoir prior to introduction of the gas into thecylinder assembly. The compressed-gas reservoir is selectively fluidlyconnected to the cylinder assembly.

Embodiments of the invention may feature one or more of the following,in any of a number of combinations. The heat-exchange subsystem mayinclude or consist essentially of a heat exchanger and a circulationapparatus for circulating a fluid from the compressed-gas reservoir tothe heat exchanger and back to the compressed-gas reservoir. The fluidmay include or consist essentially of gas stored in the compressed-gasreservoir. The circulation apparatus may include or consist essentiallyof an air pump (i.e., a pump for circulating air or other gas(es)). Theheat-exchanger may include or consist essentially of an air-to-air heatexchanger for exchanging heat between the fluid and a heat-exchange gasflowing through the heat exchanger. The heat exchanger may include orconsist essentially of an air-to-liquid heat exchanger for exchangingheat between the fluid and a heat-exchange liquid flowing through theheat exchanger. The compressed-gas reservoir may include or consistessentially of a plurality of pressure vessels serially connected suchthat the fluid is circulated through each of the pressure vessels beforecirculation to the heat exchanger.

A spray mechanism (e.g., a spray head and/or a spray rod) may bedisposed in the compressed-gas reservoir, and the fluid may include orconsist essentially of a heat-exchange fluid introduced into thecompressed-gas reservoir through the spray mechanism. The heat-exchangefluid may include or consist essentially of water. The circulationapparatus may include or consist essentially of a water pump (i.e., apump for circulating water or other liquid(s)). The compressed-gasreservoir may include or consist essentially of a pressure vessel, anaturally occurring cavern, and/or an artificially created cavern (e.g.,a mine). The heat exchanger may be in fluid communication (e.g., in acircuit different from that of the heat-exchange fluid) with an externalheating or cooling source (e.g., a thermal well). The external heatingor cooling source may include or consist essentially of a fossil fuelpower plant, a heat engine power plant, a solar thermal source, ageothermal source, an industrial process with waste heat, a heat pump, aheat source, a heat sink, and/or a source of environmentally chilledwater.

In yet another aspect, embodiments of the invention feature a method forimproving efficiency of a compressed-gas energy storage and recoverysystem. Within a cylinder assembly, gas is compressed to store energyand/or gas is expanded to recover energy. Within a compressed-gasreservoir separate from the cylinder assembly, gas is thermallyconditioned by heating gas prior to expansion and/or cooling gas aftercompression.

Embodiments of the invention may feature one or more of the following,in any of a number of combinations. Thermally conditioning gas mayinclude or consist essentially of circulating a heat-exchange fluidaround the compressed-gas reservoir to exchange heat through a wall ofthe reservoir with gas in the reservoir. The heat-exchange fluid may bethermally conditioned to maintain the heat-exchange fluid at asubstantially constant temperature. Thermally conditioning theheat-exchange fluid may include or consist essentially of exchangingheat between the heat-exchange fluid and a separate liquid and/or aseparate gas. The heat-exchange fluid may include or consist essentiallyof a liquid (e.g., water) or a gas (e.g., air such as atmospheric air).Thermally conditioning gas may include or consist essentially ofsubmerging the compressed-gas reservoir in heat-exchange liquid.Thermally conditioning gas may include or consist essentially ofintroducing (e.g., spraying) a heat-exchange fluid within thecompressed-gas reservoir to exchange heat with gas in the compressed-gasreservoir. Introducing the heat-exchange fluid may include or consistessentially of circulating the heat-exchange fluid through thecompressed-gas reservoir such that the heat-exchange fluid is not influid communication with gas in the reservoir. The heat-exchange fluidmay be circulated from a fluid reservoir containing heat-exchange fluidat a substantially constant temperature, into the compressed-gasreservoir, and back to the fluid reservoir.

The gas may be thermally conditioned within the cylinder assembly duringthe compression and/or expansion, thereby increasing efficiency of theenergy storage and recovery, and such thermal conditioning may renderthe compression and/or expansion substantially isothermal. Expanded gasmay be vented to atmosphere. Compressed gas may be stored in thecompressed-gas reservoir. Energy stored during compression of the gasmay originate from an intermittent renewable energy source (e.g., ofwind or solar energy), and energy may be recovered via expansion of thegas when the intermittent renewable energy source is nonfunctional. Thecompression and/or expansion may result in reciprocal motion of aboundary mechanism (e.g., a piston) within the cylinder assembly, andthe reciprocal motion may be converted into rotary motion (e.g., via acrankshaft or other mechanism). Thermal energy for the thermalconditioning may be recovered from an external source including orconsisting essentially of a fossil fuel power plant, a heat engine powerplant, a solar thermal source, a geothermal source, an industrialprocess with waste heat, a heat pump, a heat source, a heat sink, and/ora source of environmentally chilled water. Gas may be transferred fromthe cylinder assembly to the compressed-gas reservoir after compressionof the gas in the cylinder assembly and/or transferred from thecompressed-gas reservoir to the cylinder assembly prior to expansion ofthe gas in the cylinder assembly. The gas may be thermally conditionedduring either or both of these transfers. The compressed-gas reservoirmay be selectively fluidly connectable to the cylinder assembly (e.g.,via one or more valves and one or more conduits therebetween).

In a further aspect, embodiments of the invention feature a method forimproving efficiency of a compressed-gas energy storage and recoverysystem. Within a cylinder assembly, gas is compressed to store energyand/or gas is expanded to recover energy. Gas is transferred from thecylinder assembly after compression of the gas therein and/or to thecylinder assembly prior to expansion of the gas therein. Outside of thecylinder assembly, the gas is thermally conditioned during the transferfrom the cylinder assembly and/or the transfer to the cylinder assembly.

Embodiments of the invention may feature one or more of the following,in any of a number of combinations. Thermally conditioning the gas mayinclude or consist essentially of heating gas during the transfer to thecylinder assembly and/or cooling gas during the transfer from thecylinder assembly. The gas may be transferred to and/or from acompressed-gas reservoir, and the thermal conditioning of the gas may beperformed within the compressed-gas reservoir and/or a conduitconnecting the cylinder assembly to the compressed-gas reservoir.Thermally conditioning gas may include or consist essentially ofcirculating a heat-exchange fluid around the compressed-gas reservoir toexchange heat through a wall of the reservoir with gas in the reservoir.The heat-exchange fluid may be thermally conditioned to maintain it at asubstantially constant temperature. Thermally conditioning theheat-exchange fluid may include or consist essentially of exchangingheat between the heat-exchange fluid and a separate liquid and/or aseparate gas. The heat-exchange fluid may include or consist essentiallyof a liquid (e.g., water) and/or a gas (e.g., air such as atmosphericair). Thermally conditioning gas may include or consist essentially ofsubmerging the compressed-gas reservoir in heat-exchange liquid.Thermally conditioning gas may include or consist essentially ofspraying a heat-exchange fluid into the gas during the transfer of gasfrom and/or to the cylinder assembly. The heat-exchange fluid may besprayed into a compressed-gas reservoir and/or a conduit connecting thecylinder assembly to the compressed-gas reservoir. Thermallyconditioning gas may include or consist essentially of circulatingthrough the gas a heat-exchange fluid not in fluid communication withthe gas. The heat-exchange fluid may be circulated from a fluidreservoir containing heat-exchange fluid at a substantially constanttemperature, into the gas, and back to the fluid reservoir.

The gas may be thermally conditioned within the cylinder assembly duringthe compression and/or expansion, thereby increasing efficiency of theenergy storage and recovery, and the thermal conditioning may render thecompression and/or expansion substantially isothermal. Expanded gas maybe vented to atmosphere. Transferring gas from the cylinder assembly mayinclude or consist essentially of storing gas in a compressed-gasreservoir. Energy stored during compression of the gas may originatefrom an intermittent renewable energy source (e.g., of wind or solarenergy), and energy may be recovered via expansion of the gas when theintermittent renewable energy source is nonfunctional. The compressionand/or expansion may result in reciprocal motion of a boundary mechanism(e.g., a piston) within the cylinder assembly, and the reciprocal motionmay be converted into rotary motion (e.g., via a crankshaft or othermechanism). Thermal energy for the thermal conditioning may be recoveredfrom an external source including or consisting essentially of a fossilfuel power plant, a heat engine power plant, a solar thermal source, ageothermal source, an industrial process with waste heat, a heat pump, aheat source, a heat sink, and/or a source of environmentally chilledwater. Outside the cylinder assembly (e.g., within a compressed-gasreservoir), gas may be heated prior to expansion and/or cooled aftercompression.

These and other objects, along with advantages and features of theinvention, will become more apparent through reference to the followingdescription, the accompanying drawings, and the claims. Furthermore, itis to be understood that the features of the various embodimentsdescribed herein are not mutually exclusive and can exist in variouscombinations and permutations. Note that as used herein, the terms“pipe,” “piping” and the like shall refer to one or more conduits thatare rated to carry gas or liquid between two points. Thus, the singularterm should be taken to include a plurality of parallel conduits whereappropriate. Herein, the terms “liquid” and “water” interchangeablyconnote any mostly or substantially incompressible liquid, the terms“gas” and “air” are used interchangeably, and the term “fluid” may referto a liquid or a gas unless otherwise indicated. As used herein unlessotherwise indicated, the term “substantially” means ±10%, and, in someembodiments, ±5%. A “valve” is any mechanism or component forcontrolling fluid communication between fluid paths or reservoirs, orfor selectively permitting control or venting. The term “cylinder”refers to a chamber, of uniform but not necessarily circularcross-section, which may contain a slidably disposed piston or othermechanism that separates the fluid on one side of the chamber from thaton the other, preventing fluid movement from one side of the chamber tothe other while allowing the transfer of force/pressure from one side ofthe chamber to the next or to a mechanism outside the chamber. A“cylinder assembly” may be a simple cylinder or include multiplecylinders, and may or may not have additional associated components(such as mechanical linkages among the cylinders). The shaft of acylinder may be coupled hydraulically or mechanically to a mechanicalload (e.g., a hydraulic motor/pump or a crankshaft) that is in turncoupled to an electrical load (e.g., rotary or linear electricmotor/generator attached to power electronics and/or directly to thegrid or other loads), as described in the '595 and '853 applications.Herein, the terms “heat-transfer” and “heat-exchange” are usedinterchangeably.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the sameparts throughout the different views. Cylinders, rods, and othercomponents are depicted in cross section in a manner that will beintelligible to all persons familiar with the art of pneumatic andhydraulic cylinders. Also, the drawings are not necessarily to scale,emphasis instead generally being placed upon illustrating the principlesof the invention. In the following description, various embodiments ofthe present invention are described with reference to the followingdrawings, in which:

FIG. 1 is a schematic of various components of an energy storage andrecovery system in accordance with various embodiments of the invention,and illustrating an application where waste heat from a power plant isused to heat stored compressed gas prior to and/or during expansion inthe system;

FIG. 2 is a schematic cross-section of a cylinder with a closed-loopliquid-injection system within a compressed-air energy storage andrecovery system in accordance with various embodiments of the invention;

FIGS. 3 and 4 are schematic diagrams of compressed-gas storagesubsystems for heating and cooling compressed gas in energy-conversionsystems in accordance with various embodiments of the invention;

FIG. 5 is a schematic diagram of a compressed-gas storage subsystem forheating and cooling compressed gas in energy-conversion systems via aircirculation and air-to-air heat exchange in accordance with variousembodiments of the invention;

FIG. 6 is a schematic diagram of a compressed-gas storage subsystem forheating and cooling compressed gas in energy-conversion systems vialiquid circulation and liquid-to-air heat exchange in accordance withvarious embodiments of the invention;

FIG. 7 is a schematic diagram of a compressed-gas storage subsystem forheating and cooling compressed gas in energy-conversion systems via aircirculation and air-to-air heat exchange in accordance with variousembodiments of the invention; and

FIGS. 8 and 9 are schematic diagrams of compressed-gas storagesubsystems for heating and cooling compressed gas in energy-conversionsystems via liquid circulation and liquid-to-air heat exchange inaccordance with various embodiments of the invention.

DETAILED DESCRIPTION

FIG. 1 is a diagram of various components of an energy storage andrecovery system in accordance with various embodiments of the invention.The illustrated system includes or consists essentially of aninstallation 100 where thermal energy is available for recovery,extracted from the surroundings, needed for usage, and/or may be removedfor cooling. Example installations 100 include fossil-fuel based powerplants (e.g., coal, natural gas); other heat-engine based power plantssuch as nuclear, solar thermal, and geothermal; industrial processeswith waste heat; heat pumps, heat sources, and heat sinks; buildingsneeding space heating or cooling; and sources of environmentally chilledwater. In FIG. 1, for illustrative purposes, a power plant 102 is shownwhose excess thermal energy is recoverable through a standardheat-exchange unit 104. Generated power 106 from the power plant 102 maybe used to drive the compressed-gas energy storage system 108 asdetermined by the operator (e.g., when market demand for power is low),storing energy in the form of compressed gas in pressure vessels 110,caverns, or other means of high-pressure gas storage. Upon demand forincreased power, this stored energy in the form of compressed gas inpressure vessels 110 undergoes expansion (e.g., staged expansion) in thecompressed-gas energy storage system 108 to generate power for usage(e.g., power grid delivery 112). The recovered thermal energy from thepower plant 102 may be used in the heat-exchange subsystem of thecompressed-gas pressure vessels 110 (or other pressurized storage) topreheat the stored compressed gas and/or to heat the heat-exchange fluidand gas during expansion, increasing the work done by a given volume ofpressurized gas and improving system efficiency and/or performance.Likewise, but not illustrated herein, water cooled by heat exchange withcold environments, ground loops, or water loops, or other lowtemperature reservoirs may be used in the heat-exchange subsystem topre-cool and/or continually cool the compressed gas prior to and duringfurther compression, improving system efficiency and/or performance. Inall these instances, performance and/or value of the system may bemarkedly improved.

FIG. 2 illustrates a pneumatic cylinder with a closed-loopwater-injection system within a compressed air energy storage andrecovery system 200. The system 200 includes a cylinder assembly 202, aheat-transfer subsystem 204, and a control system 205 for controllingoperation of the various components of system 200. During systemoperation, compressed air is either directed into vessel 206 (e.g., oneor more pressure vessels or naturally occurring formations such ascaverns) during storage of energy or released from vessel 206 duringrecovery of stored energy. Air is admitted to the system 200 throughvent 208 during storage of energy, or exhausted from the system 200through vent 208 during release of energy.

The control system 205 may be any acceptable control device with ahuman-machine interface. For example, the control system 205 may includea computer (for example a PC-type) that executes a stored controlapplication in the form of a computer-readable software medium. Moregenerally, control system 205 may be realized as software, hardware, orsome combination thereof. For example, controller 205 may be implementedon one or more computers, such as a PC having a CPU board containing oneor more processors such as the Pentium, Core, Atom, or Celeron family ofprocessors manufactured by Intel Corporation of Santa Clara, Calif., the680x0 and POWER PC family of processors manufactured by MotorolaCorporation of Schaumburg, Ill., and/or the ATHLON line of processorsmanufactured by Advanced Micro Devices, Inc., of Sunnyvale, Calif. Theprocessor may also include a main memory unit for storing programsand/or data relating to the methods described above. The memory mayinclude random access memory (RAM), read only memory (ROM), and/or FLASHmemory residing on commonly available hardware such as one or moreapplication specific integrated circuits (ASIC), field programmable gatearrays (FPGA), electrically erasable programmable read-only memories(EEPROM), programmable read-only memories (PROM), programmable logicdevices (PLD), or read-only memory devices (ROM). In some embodiments,the programs may be provided using external RAM and/or ROM such asoptical disks, magnetic disks, as well as other commonly storagedevices.

For embodiments in which the functions of controller 205 are provided bysoftware, the program may be written in any one of a number of highlevel languages such as FORTRAN, PASCAL, JAVA, C, C++, C#, LISP, PERL,BASIC or any suitable programming language. Additionally, the softwarecan be implemented in an assembly language and/or machine languagedirected to the microprocessor resident on a target device.

The control system 205 may receive telemetry from sensors monitoringvarious aspects of the operation of system 200 (as described below), andmay provide signals to control valve actuators, valves, motors, andother electromechanical/electronic devices. Control system 205 maycommunicate with such sensors and/or other components of system 200 viawired or wireless communication. An appropriate interface may be used toconvert data from sensors into a form readable by the control system 205(such as RS-232 or network-based interconnects). Likewise, the interfaceconverts the computer's control signals into a form usable by valves andother actuators to perform an operation. The provision of suchinterfaces, as well as suitable control programming, is clear to thoseof ordinary skill in the art and may be provided without undueexperimentation.

The cylinder assembly 202 includes a piston 210 (or other suitableboundary mechanism) slidably disposed therein with a center-drilled rod212 extending from piston 210 and preferably defining a fluidpassageway. The piston 210 divides the cylinder assembly 202 into afirst chamber (or “compartment”) 214 and a second chamber 216. The rod212 may be attached to a mechanical load, for example, a crankshaft orhydraulic system. Alternatively or in addition, the second chamber 216may contain hydraulic fluid that is coupled through other pipes 218 andvalves to a hydraulic system 220 (which may include, e.g., a hydraulicmotor/pump and an electrical motor/generator). The heat-transfersubsystem 204 includes or consists essentially of a heat exchanger 222and a booster-pump assembly 224.

At any time during an expansion or compression phase of gas within thefirst or upper chamber 214 of the cylinder assembly 202, the chamber 214will typically contain a gas 226 (e.g., previously admitted from storagevessel 206 during the expansion phase or from vent 208 during thecompression phase) and (e.g., an accumulation of) heat-transfer fluid228 at substantially equal pressure P_(s) (e.g., up to approximately3,000 psig). The heat-transfer fluid 228 may be drawn through thecenter-drilled rod 212 and through a pipe 230 by the pump 224. The pump224 raises the pressure of the heat-transfer fluid 228 to a pressureP_(i)′ (e.g., up to approximately 3,015 psig) somewhat higher thanP_(s), as described in U.S. patent application Ser. No. 13/009,409,filed on Jan. 19, 2011 (the '409 application), the entire disclosure ofwhich is incorporated by reference herein. The heat-transfer fluid 228is then sent through the heat exchanger 222, where its temperature isaltered, and then through a pipe 232 to a spray mechanism 234 disposedwithin the cylinder assembly 202. In various embodiments, when thecylinder assembly 202 is operated as an expander, a spray 236 of theheat-transfer fluid 228 is introduced into the cylinder assembly 202 ata higher temperature than the gas 226 and, therefore, transfers thermalenergy to the gas 226 and increases the amount of work done by the gas226 on the piston 210 as the gas 226 expands. In an alternative mode ofoperation, when the cylinder assembly 202 is operated as a compressor,the heat-transfer fluid 228 is introduced at a lower temperature thanthe gas 226. Control system 205 may enforce substantially isothermaloperation, i.e., expansion and/or compression of gas in cylinderassembly 202, via control over, e.g., the introduction of gas into andthe exhausting of gas out of cylinder assembly 202, the rates ofcompression and/or expansion, and/or the operation of heat-transfersubsystem 204 in response to sensed conditions. For example, controlsystem 205 may be responsive to one or more sensors disposed in or oncylinder assembly 202 for measuring the temperature of the gas and/orthe heat-transfer fluid within cylinder assembly 202, responding todeviations in temperature by issuing control signals that operate one ormore of the system components noted above to compensate, in real time,for the sensed temperature deviations. For example, in response to atemperature increase within cylinder assembly 202, control system 205may issue commands to increase the flow rate of spray 236 ofheat-transfer fluid 228.

The circulating system 224 described above will typically have higherefficiency than a system which pumps liquid from a low intake pressure(e.g., approximately 0 psig) to P_(i)′, as detailed in the '409application. In some embodiments, the heat-transfer fluid 228 (and/orother heat-transfer fluids described herein) incorporates one or moreadditives and/or solutes in order to, e.g., reduce the solubility of thegas therein and/or to slow the dissolution of the gas therein, reduce orotherwise alter the surface tension of the heat-transfer fluid, retardor prevent corrosion, enhance lubricity, and/or prevent formation of orkill microorganisms such as bacteria, as described in U.S. patentapplication Ser. No. 13/082,808, filed Apr. 8, 2011 (the '808application), the entire disclosure of which is incorporated byreference herein.

Furthermore, embodiments of the invention may be applied to systems inwhich chamber 214 is in fluid communication with a pneumatic chamber ofa second cylinder (rather than with vessel 206). That second cylinder,in turn, may communicate similarly with a third cylinder, and so forth.Any number of cylinders may be linked in this way. These cylinders maybe connected in parallel or in a series configuration, where thecompression and expansion is done in multiple stages.

The fluid circuit of heat exchanger 222 may be filled with water, acoolant mixture, and/or any acceptable heat-transfer medium. Inalternative embodiments, a gas, such as air or refrigerant, is used asthe heat-transfer medium. In general, the fluid is routed by conduits toa large reservoir of such fluid in a closed or open loop. One example ofan open loop is a well or body of water from which ambient water isdrawn and the exhaust water is delivered to a different location, forexample, downstream in a river. In a closed-loop embodiment, a coolingtower may cycle the water through the air for return to the heatexchanger. Likewise, water may pass through a submerged or buried coilof continuous piping where a counter heat-exchange occurs to return thefluid flow to ambient temperature before it returns to the heatexchanger for another cycle.

In various embodiments, the heat-exchange fluid is conditioned (i.e.,pre-heated and/or pre-chilled) or used for heating or cooling needs byconnecting the fluid inlet 238 and fluid outlet 240 of the external heatexchange side of the heat exchanger 222 to an installation, such as aheat-engine power plant, an industrial process with waste heat, a heatpump, and/or a building needing space heating or cooling, as describedabove and in the '513 application. The installation may be a large waterreservoir that acts as a constant-temperature thermal fluid source foruse with the system. Alternatively, the water reservoir may be thermallylinked to waste heat from an industrial process or the like, asdescribed above, via another heat exchanger contained within theinstallation. This allows the heat-transfer fluid to acquire or expelheat from/to the linked process, depending on configuration, for lateruse as a heating/cooling medium in the compressed air energystorage/conversion system.

The heat-transfer subsystems similar to those discussed above and/ordepicted in FIG. 2 may also be used in conjunction with thehigh-pressure gas-storage systems (e.g., vessel 206) to thermallycondition the pressurized gas stored therein, as shown in FIGS. 3 and 4.FIG. 3 depicts a heat-transfer subsystem 300 incorporating a gas storagesystem for use with the compressed-gas energy conversion systemsdescribed herein, to expedite transfer of thermal energy to, forexample, the compressed gas prior to and during expansion. Compressedgas from the pressure vessels (302 a-302 d) is circulated through a heatexchanger 304 using an air pump 306 operating as a circulator. The airpump 306 operates with a small pressure change sufficient forcirculation, but within a housing that is able to withstand highpressures, as detailed in the '409 application. The air pump 306circulates the high-pressure air through the heat exchanger 304 withoutsubstantially increasing its pressure (e.g., a 50 psi increase for 3,000psi air). In this way, the stored compressed air may be pre-heated (orpre-cooled) by opening valve 308 with valve 310 closed and heated duringexpansion or cooled during compression by closing valve 308 and openingvalve 310. Valve 310, when open, places the subsystem 300 in fluidcommunication with an energy-storage system such as system 200 in FIG.2; in FIG. 2, the gas storage vessel 206 may be replaced by a subsystemsuch as subsystem 300 in FIG. 3. The heat exchanger 304 may be any sortof standard heat-exchanger design; illustrated here is a tube-in-shelltype heat exchanger with high-pressure air inlet and outlet ports 312and 314 and low-pressure shell ports 316 and 318 (which may be connectedto an external heating or cooling source, as described above).

Preheating a particular mass of compressed air in a fixed volume such aspressure vessels 302 a-302 d will generally increase the pressure of thecompressed air and thus the stored potential energy. Upon expansion,more energy will be recovered from the compressed air, essentiallyrecuperating energy from the heat source (e.g., waste heat, processheat, ground loop); also, the final temperature of the expanded air willbe higher than when the initial compressed air is at ambienttemperature. Likewise, cooling of the stored compressed gas willgenerally decrease the pressure and thus reduce the work necessary tocompress more gas into pressure vessels 302 a-302 d. Thus, bypre-cooling the stored compressed gas and cooling the gas duringcompression, relatively less energy will be required in the compressionphase. When the stored compressed gas later increases in temperature(e.g., by deliberate preheating), the energy stored in 302 a-302 d willincrease. The vessels 302 a-302 d are depicted in FIG. 3 in a horizontalposition but other orientations are contemplated and within the scope ofthe invention.

In addition to the efficiency improvements enabled by pre-heating (orpre-cooling) the gas stored in a compressed-gas reservoir, systemefficiency may be enhanced by thermally conditioning gas outside of thecylinder assembly during its transfer to and/or from the cylinderassembly, e.g., during the transfer of gas from and/or to acompressed-gas reservoir, as such transfers may result in temperaturechanges of the gas outside of the cylinder assembly (e.g., in thereservoir) in the absence of active heat exchange. For example, the gasmay be heated or cooled in the compressed-gas reservoir (e.g., reservoir206 in FIG. 2) and/or in one or more conduits connecting thecompressed-gas reservoir with the cylinder assembly (e.g., pipe 240 inFIG. 2). Heating and/or cooling in conduits may be accomplished withheat-transfer subsystems like those described herein for use withcompressed-gas reservoirs, e.g., a conduit may be heated and/or cooledfrom its exterior (or even submerged) and/or may have heat-exchangefluid introduced (e.g., sprayed) therein.

During exemplary compression and expansion cycles in a cylinderassembly, most (up to approximately 90%, or even more) of thecompression or expansion of the gas occurs within the cylinder assembly,and the remainder of the compression or expansion generally occurswithin the compressed-gas reservoir (and/or a connecting conduit) as thegas is stored or released for the cycle performed within the cylinderassembly. This compression and/or expansion within the reservoir may besubstantially isobaric (the pressure change within the reservoirgenerally depends on the relative volumes of the cylinder assembly andthe compressed-gas reservoir and/or the masses of gas therewithin; thus,while some finite change of gas pressure generally occurs, the changemay be small when considered over the volume of the typically largerreservoir), but may involve temperature changes of the gas outside ofthe cylinder assembly (e.g., in the reservoir) in the absence of activeheat exchange even if the compression and/or expansion within thecylinder assembly is substantially isothermal. Thus, any of theembodiments described herein for thermal conditioning of gas stored in acompressed-gas reservoir may also or alternatively be utilized to heator cool gas during transfers into and out of the cylinder assembly. Suchthermal conditioning advantageously minimizes or prevents temperaturechanges within the compressed-gas reservoir during transfer stages,improving total system efficiency. The above-described thermalconditioning outside of the cylinder assembly may be performed inconjunction with lessening or stopping any thermal conditioning beingperformed inside the cylinder assembly itself during the transfers outof and into the cylinder assembly, as described in the '808 application,as at least a portion of the expansion and/or compression during thetransfers may be taking place outside of the cylinder assembly (e.g.,within a compressed-gas reservoir).

FIG. 4 is a schematic of an alternative compressed-air pressure vesselsubsystem 400 for heating and cooling of compressed gas in energystorage systems, to expedite transfer of thermal energy to and from thecompressed gas prior to and/or during expansion or compression. Asdepicted, thermal energy transfer to and from stored compressed gas inpressure vessels 402, 404 is expedited via water circulation using awater pump 406 and heat exchanger 408. The water pump 406 operates witha small pressure change sufficient for circulation and spray, but withina housing that is able to withstand high pressures. That is, itcirculates high-pressure water (or other suitable heat-transfer fluid)through heat exchanger 408 and introduces the water into pressurevessels 402 and 404 without substantially increasing its pressure (e.g.,a 100 psi increase for circulating and spraying within 3,000 psi storedcompressed air). In this way, the stored compressed air may bepre-heated (or pre-cooled) using a water circulation and sprayingpumping method, which also may allow for active water monitoring of thepressure vessels 402 and 404. The spray heat exchange may occur aspre-heating prior to expansion and/or pre-cooling prior to compressionin the system 400 when valve 410 is opened. The heat exchanger 408 maybe any sort of standard heat exchanger design; illustrated here is atube-in-shell heat exchanger with high-pressure water inlet and outletports 412 and 414 and low-pressure shell water ports 416 and 418. Theshell water ports 416 and 418 may permit communication with a secondheat exchanger or a thermal well or some other body of fluid. Asliquid-to-liquid heat exchangers tend to be more efficient thanair-to-liquid heat exchangers, heat-exchanger size may be reduced and/orheat transfer may be improved by use of a liquid-to-liquid exchanger.

Heat exchange within the pressure vessels 402, 404 is expedited byactive spraying of liquid (e.g., water) into the vessels 402,404. Asillustrated in FIG. 4, perforated spray rods 420 and 422 may beinstalled within pressure vessels 402 and 404. Water pump 406 increasesthe water pressure above the vessel pressure such that water is activelycirculated and sprayed out of spray rods 420, 422, as shown by arrows424 and 426. After spraying through the volumes of vessels 402 and 404,water 428, 430 may accumulate at the bottom of the vessels 402, 404 andthen be removed through ports 432, 434 and piping 436. The piping 436returns the water 428, 430 to the heat exchanger 408, through which thewater 428, 430 is circulated as part of the closed-loop watercirculation and spray system. Valve 410, when open, places the subsystem400 in fluid communication with an energy-storage system such as system200 in FIG. 2; in FIG. 2, the gas storage vessel 206 may be replaced bya subsystem such as subsystem 400 in FIG. 4.

The vessels 402, 404 and their internal spray mechanisms 420, 422 aredepicted in FIG. 4 in a horizontal position but other orientations arecontemplated and within the scope of the invention. Other spraymechanisms (e.g., spray-head type) are also contemplated and within thescope of the invention. Two pressure vessels 402, 404 are depicted inFIG. 4 but other numbers of vessels and other types of gas storage(e.g., natural or artificial caverns) are contemplated and within thescope of the invention.

FIG. 5 is a schematic of an alternative compressed-air pressure vesselsubsystem 500 for heating and cooling of compressed gas in energystorage systems, to expedite transfer of thermal energy to and from thecompressed gas prior to and/or during expansion or compression. Thermalenergy transfer to and/or from stored compressed gas in pressure vessels502 is expedited via air circulation using an enclosure 504 and aircirculation fans 506. In the subsystem 500, air enters the enclosure 504through vents 508. The air may be at a temperature different from thecompressed gas within the vessels 502. The vessels 502 are in anarrangement that permits substantial circulation of air around andbetween them. Air circulating around and between the vessels 502 gainsthermal energy from the vessels 502 if the air entering through thevents 508 is at a lower temperature than the gas within the vessels 502;similarly, the vessels 502 gain thermal energy from the air if the airentering through the vents 508 is at a higher temperature than the gaswithin the vessels 502. Air that has circulated around and between thevessels 502 is typically pulled from the enclosure 504 by fans 506. Theair exhausted by fans 506 may be confined by one or more ducts (notshown), circulated through a heat-exchange system to change itstemperature, and returned to the vents 508 through the ducts.

Valves and piping (not shown) may place the contents of the vessels 502in fluid communication with an energy-storage system such as system 200in FIG. 2; in FIG. 2, the gas storage vessel 206 may be replaced by asubsystem such as subsystem 500 in FIG. 5. The vessels 502 are depictedin FIG. 5 in a horizontal position but other orientations arecontemplated and within the scope of the invention. Six vessels 502 aredepicted in FIG. 5 but other numbers of vessels, as well as other typesof gas storage (e.g., natural or artificial caverns), are contemplatedand within the scope of the invention.

FIG. 6 is a schematic of yet another compressed-air pressure vesselsubsystem 600 for use with heating and cooling of compressed gas inenergy storage systems, to expedite transfer of thermal energy to andfrom the compressed gas prior to and/or during expansion or compression.Thermal energy transfer to and from stored compressed gas in pressurevessels 602 is expedited via circulation of one or more liquids (e.g.,water) in an enclosure 604 and using piping 606, 608 to respectivelyadmit liquid to and remove liquid from the enclosure 604. In theexemplary subsystem 600 depicted in FIG. 6, the liquid level 610 inenclosure 604 is indicated by closely-spaced vertical lines. Liquidenters the enclosure 604 through pipe 606. The liquid may be at atemperature different from that of the compressed gas within the vessels602. The vessels 602 are preferably in an arrangement that permitssubstantial circulation of water around and between them. Liquidcirculating around and between the vessels 602 gains thermal energy fromthe vessels 602 if the liquid entering through pipe 606 is at a lowertemperature than the gas within the vessels 602; similarly, the vessels602 gain thermal energy from the liquid if the liquid entering throughthe pipe 606 is at a higher temperature than the gas within the vessels602. Liquid that has circulated around and between the vessels 602 isremoved from the enclosure through pipe 608. The liquid removed throughpipe 608 may be circulated through a heat-exchange system (not shown inFIG. 6) to change its temperature and returned to the enclosure 604through pipe 606.

Valves and piping (not shown) may place the contents of the vessels 602in fluid communication with an energy-storage system such as system 200in FIG. 2; in FIG. 2, the gas storage vessel 206 may be replaced by asubsystem such as subsystem 600 in FIG. 6. The vessels 602 are depictedin FIG. 6 in a horizontal position but other orientations arecontemplated and within the scope of the invention. Six vessels 602 aredepicted in FIG. 6 but other numbers of vessels are contemplated andwithin the scope of the invention.

FIG. 7 depicts a compressed-air pressure vessel subsystem 700 forheating and cooling of compressed gas in energy-storage systems, toexpedite transfer of thermal energy to and from the compressed gas priorto and/or during expansion or compression. Thermal energy transfer toand/or from stored compressed gas in pressure vessels 702 is expeditedvia gas circulation. In the exemplary subsystem 700 depicted in FIG. 7,the vessels 702 are interconnected by piping 704 and, in someembodiments, valves (not shown) so that gas may enter the set of vessels702 through one port (e.g., port 706), circulate or travel through theset of vessels 702, and exit the set of vessels 702 through a secondport (e.g., port 708). The gas may be at any pressure tolerated by thevessels 702 (e.g., between 0 psig and 3,000 psig). If valve 710 is openand valve 712 is closed, gas may flow from port 708, through piping 714,and through an gas-to-gas (e.g., air-to-air) heat exchanger 716. In theheat exchanger 716, air from the vessels 702 exchanges heat with air 718that may be forced through the heat exchanger 716 by a fan or othercirculation mechanism (not shown), raising or lowering the temperatureof the air from the vessels 702. The air 718 forced through the heatexchanger 716 may in turn be passed through a second heat-exchangesystem to regulate its temperature. Gas from the vessels 702 passingthrough the heat exchanger 716 loses thermal energy if the external air718 passing through the heat exchanger 716 is at a lower temperaturethan the gas within the vessels 702; similarly, gas from the vessels 702passing through the heat exchanger 716 gains thermal energy if theexternal air 718 passing through the heat exchanger 716 is at a highertemperature than the gas within the vessels 702. Air is drawn from theheat exchanger 716 through piping 720 by an air pump 722 and returned tothe vessels 704 through port 706.

Valve 712 may place the contents of the vessels 702 in fluidcommunication with an energy-storage system such as system 200 in FIG.2; in FIG. 2, the gas storage vessel 206 may be replaced by a subsystemsuch as subsystem 700 in FIG. 7. The vessels 702 are depicted in FIG. 7in a horizontal position but other orientations are contemplated andwithin the scope of the invention. Four vessels 702 are depicted in FIG.7 but other numbers of vessels, as well as other types of gas storage(e.g., natural or artificial caverns), are contemplated and within thescope of the invention.

FIG. 8 depicts a compressed-air pressure vessel subsystem 800 forheating and cooling of compressed gas in energy storage systems, toexpedite transfer of thermal energy to and from the compressed gas priorto and/or during expansion or compression. Thermal energy transfer toand/or from stored compressed gas in a pressure vessel 802 is expeditedvia circulation of a liquid (e.g., water). This liquid may be at nearatmospheric pressure even when compressed gas within vessel 802 is atsuper-atmospheric or higher pressures (e.g., 3000 psi). In the exemplarysubsystem 800 depicted in FIG. 8, liquid from a thermal reservoir orpool 804, which may be at or near atmospheric pressure, is pulled by awater pump 806 through pipe 808 and pushed through pipe 810 to a port812 in the end-cap of the vessel 802. Within the vessel 802, water flowfrom pipe 810 continues through pipe 814, to which are attachedheat-exchange fins 816 or other protuberances or contrivances forenhancing heat exchange. Pipe 814 follows a path within vessel 802 thatenables gas within the vessel 802 to circulate around the piping 814 andits heat-exchange fins 816. Pipe 814 terminates at a port 818 in theend-cap of the vessel 802. Liquid flow continues from pipe 814 throughpipe 820, returning water to the thermal reservoir 804.

Water (or other liquid) enters the storage vessel 802 through pipe 810and 814. The water may be at a temperature different from the compressedgas within the vessel 802. The piping 814 is arranged to permitsubstantial heat transfer to the air in the vessel 802. Watercirculating in the piping 814 gains thermal energy from the vessel 802if the water entering through pipes 810 and 814 is at a lowertemperature than the gas within the vessel 802; similarly, the gas inthe vessel 802 gains thermal energy from the water in pipe 814 if thewater entering through the pipes 810 and 814 is at a higher temperaturethan the gas within the vessel 802. Water that has circulated within thevessel 802 is removed from the enclosure through pipe 820. The waterremoved through pipe 820 may be circulated through a heat-exchangesystem (not shown) to change its temperature and returned to the vessel802 through pipe 810.

Valves and piping (not shown) may place the contents of the vessel 802in fluid communication with an energy-storage system such as system 200in FIG. 2; in FIG. 2, the gas storage vessel 206 may be replaced by asubsystem such as subsystem 800 in FIG. 8. The vessel 802 is depicted inFIG. 8 in a horizontal position but other orientations are contemplatedand within the scope of the invention. One vessel 802 is depicted inFIG. 8 but other numbers of vessels, as well as other types of gasstorage (e.g., natural or artificial caverns), are contemplated andwithin the scope of the invention.

FIG. 9 illustrates another compressed-air pressure vessel subsystem 900for heating and cooling of compressed gas in energy-storage systems, toexpedite transfer of thermal energy to and from the compressed gas priorto and/or during expansion or compression. Thermal energy transfer toand from stored compressed gas in a cavern 902 (e.g., a naturallyoccurring or artificially created cavern, which may be locatedunderground) is expedited via liquid circulation using a water pump 904and heat exchanger 906. The water pump 904 operates with a smallpressure change sufficient for circulation and spray, but within ahousing that is able to withstand high pressures; pump 904 circulateshigh-pressure water through heat exchanger 906 and then to a spraymechanism 908, creating a spray 910 inside the cavern 902 withoutsubstantially increasing the pressure of the liquid (e.g., a 100 psiincrease for circulating and spraying within 3,000 psi stored compressedair). In this way, the stored compressed air may be pre-heated (orpre-cooled) using a water circulation and spraying method, which alsomay allow for active water monitoring of the storage cavern 902. Thespray heat exchange may occur as pre-heating prior to expansion and/orpre-cooling prior to compression. The heat exchanger 906 may be of anystandard heat exchanger design; illustrated here is a tube-in-shell heatexchanger with high-pressure water inlet and outlet ports 912 and 914and low-pressure shell water ports 916 and 918. The shell water ports916 and 918 may permit communication with a second heat exchanger or athermal well or some other body of fluid. Heat exchange within thestorage cavern 902 is expedited by active spraying 910 of liquid (e.g.,water) into the cavern 902. Illustrated in FIG. 9 is a scheme where oneor more perforated spray heads 908 are installed within the storagecavern 902. Water pump 906 increases the water pressure above the vesselpressure such that water is actively circulated and sprayed out of sprayhead 908. After spraying through much or all of the volume of cavern902, water 920 may accumulate at the bottom of the cavern 902 and thenbe removed through piping 922. The piping 922 returns the water 920 tothe pump 904 and heat exchanger 906, through which the water iscirculated as part of the closed-loop water circulation and spraysystem. A valve or valves and piping (not shown) may place thegas-filled portion of cavern 902 in fluid communication with anenergy-storage system such as system 200 in FIG. 2; in FIG. 2, the gasstorage vessel 206 may be replaced by a subsystem such as subsystem 900in FIG. 9.

If the cavern 902 is of sufficient size, a substantial mass of water 920may be allowed to accumulate at the bottom of the cavern 902. In thiscase, this mass of water 920 may exchange heat relatively slowly withthe air also contained in cavern 902, and may be used as a thermalreservoir. A vertical cavern shape and spray-head-type internal spraymechanism 908 are depicted in FIG. 9 but other orientations and spraymechanisms (e.g., spray rod, multiple nozzles) are contemplated andwithin the scope of the invention. A single cavern 902 is depicted inFIG. 4 but other numbers of caverns and storage volumes comprisingcaverns and other forms of gas storage (e.g., pressure vessels) arecontemplated and within the scope of the invention.

Generally, the systems described herein may be operated in both anexpansion mode and in the reverse compression mode as part of afull-cycle energy storage system with high efficiency. For example, thesystems may be operated as both compressor and expander, storingelectricity in the form of the potential energy of compressed gas andproducing electricity from the potential energy of compressed gas.Alternatively, the systems may be operated independently as compressorsor expanders.

The terms and expressions employed herein are used as terms ofdescription and not of limitation, and there is no intention, in the useof such terms and expressions, of excluding any equivalents of thefeatures shown and described or portions thereof, but it is recognizedthat various modifications are possible within the scope of theinvention claimed.

1. A method for improving efficiency of a compressed-gas energy storageand recovery system, the method comprising: (i) receiving energy from apower source comprising an electric generating plant or a source ofrenewable energy, receiving gas from an ambient atmosphere, storing thereceived energy in the form of compressed gas by compressing the gaswithin a cylinder assembly, and transferring compressed gas to acompressed-gas reservoir to store the compressed gas; and (ii)transferring compressed gas from the compressed-gas reservoir to thecylinder assembly, expanding the compressed gas within the cylinderassembly to recover energy from the compressed gas, venting expanded gasto an ambient atmosphere, and converting the recovered energy intoelectricity; and outside of the cylinder assembly, thermallyconditioning the gas, via heat exchange with a heat-exchange fluid,during at least one of transferring compressed gas from thecompressed-gas reservoir or transferring compressed gas to thecompressed-gas reservoir.
 2. The method of claim 1, wherein thermallyconditioning the gas comprises at least one of (i) heating compressedgas during the transfer from the compressed-gas reservoir or (ii)cooling compressed gas during the transfer to the compressed-gasreservoir.
 3. The method of claim 1, wherein the thermal conditioning ofthe gas is performed within the compressed-gas reservoir.
 4. The methodof claim 1, wherein the thermal conditioning of the gas is performedwithin a conduit connecting the cylinder assembly to the compressed-gasreservoir.
 5. The method of claim 1, wherein thermally conditioning gascomprises circulating the heat-exchange fluid around the compressed-gasreservoir to exchange heat through a wall thereof with gas in thecompressed-gas reservoir.
 6. The method of claim 5, further comprisingthermally conditioning the heat-exchange fluid to maintain theheat-exchange fluid at a substantially constant temperature.
 7. Themethod of claim 6, wherein thermally conditioning the heat-exchangefluid comprises exchanging heat between the heat-exchange fluid and aseparate liquid.
 8. The method of claim 6, wherein thermallyconditioning the heat-exchange fluid comprises exchanging heat betweenthe heat-exchange fluid and a separate gas.
 9. The method of claim 1,wherein thermally conditioning gas comprises submerging thecompressed-gas reservoir in heat-exchange liquid.
 10. The method ofclaim 1, wherein thermally conditioning gas comprises spraying theheat-exchange fluid into the gas during the at least one of transferringgas from the compressed-gas reservoir or transferring gas to thecompressed-gas reservoir.
 11. The method of claim 10, wherein theheat-exchange fluid is sprayed into the compressed-gas reservoir. 12.The method of claim 1, wherein thermally conditioning gas comprisescirculating the heat-exchange fluid through the gas, the heat-exchangefluid not in fluid communication with the gas.
 13. The method of claim12, wherein the heat-exchange fluid is circulated (i) from a fluidreservoir containing heat-exchange fluid at a substantially constanttemperature, (ii) into the gas, and (iii) back to the fluid reservoir.14. The method of claim 1, further comprising thermally conditioning thegas within the cylinder assembly during at least one of the compressionor the expansion, thereby increasing efficiency of the energy storageand recovery.
 15. The method of claim 14, wherein the thermallyconditioning the gas during at least one of the compression or theexpansion renders the at least one of the compression or the expansionsubstantially isothermal.
 16. The method of claim 1, wherein (i) energystored during compression of the gas originates from an intermittentrenewable energy source of wind or solar energy, and (ii) energy isrecovered via expansion of the gas when the intermittent renewableenergy source is nonfunctional.
 17. The method of claim 1, wherein theexpansion results in reciprocal motion of a boundary mechanism withinthe cylinder assembly, and further comprising converting the reciprocalmotion into rotary motion.
 18. The method of claim 1, furthercomprising, outside the cylinder assembly, at least one of (i) heatinggas prior to the expansion thereof or (ii) cooling gas after thecompression thereof.
 19. The method of claim 18, wherein the at leastone of (i) heating gas prior to the expansion thereof or (ii) coolinggas after the compression thereof is performed within the compressed-gasreservoir.
 20. The method of claim 1, wherein: (i) the gas is compressedwithin the cylinder assembly to a first pressure, and furthercomprising, prior to transfer to the compressed-gas reservoir,transferring the gas to a second cylinder assembly and compressing thegas within the second cylinder assembly from the first pressure to asecond pressure larger than the first pressure; or (ii) the gas isexpanded within the cylinder assembly to a first pressure, and furthercomprising, prior to venting expanded gas to the ambient atmosphere,transferring the gas to a second cylinder assembly and expanding the gaswithin the second cylinder assembly from the first pressure to a secondpressure smaller than the first pressure.